Well, I can't figure out what is causing the build to fail, and it isn't really that important to have it working anyway, so I gave up. Plus, I ran into a very weird situation this morning when I opened up my F# project, and it was dog-slow. I uninstalled the VS 2005 SDK, and then all was well with my F# project. Oh, well - until there's a binary/MSI distribution of the IronPython VS integration piece, I'm not going to try anymore. I know others have been able to get it to work...sometimes you win, and sometimes it's better to win in other ways. In this case, I'll just use ipy.exe and move on.